Ion doping or implanting apparatuses have been used for adding electroactive elements to a semiconductor or adding atoms of an additive to a substrate for adhesive joining of hardly adhesive material to the substrate.
Up to the present, however, there have been no ion mass separating, ion doping apparatus using an ion beam larger in size (for example, 300 mm×800 mm). Conventionally employed in ion doping apparatuses is a non-mass-separation system using an ion beam for ion doping without ion mass separation or a magnetic filter system using a magnetic filter for simple reduction in ratio of lighter ion species (for example, hydrogen ions) in a plasma generating portion of an ion generator.
For example, in an ion doping apparatus for a semiconductor, hydrogen-diluted phosphine (PH3) or diborane (B2H6) is used as plasma-generating source gas for an ion generator, which generates not only desired PHx and B2Hx but also ion species such as Hx, P2Hx and BHx in the plasma generating portion, a mixed beam of such ion species being extracted from the plasma generating portion. Such existence of the ion species other than the desired ones will lead to a problem of nonuniformity in implantation depth distribution of P and B through ion doping as well as a problem of imparting extra thermal load to a substrate.
Accordingly, it has been desired to promptly establish technique for stable mass separation in an ion beam larger in size and particularly broader in width.
Meanwhile, there have been envisaged ion mass separators for ion beams smaller in size. FIGS. 1 and 2 show an example of an ion mass separator for an ion beam smaller in size. In this ion mass separator 1, ions generated in a plasma generating portion (not shown) are extracted and accelerated by ion extraction electrodes 3 into an ion beam 4 which is guided to a small-sized, vacuum ion deflection pathway 5 via an inlet 6 at one end thereof. Arranged outside of an intermediate portion of the ion deflection pathway 5 is an electro-magnet 8 comprising an iron core 7a with a solenoid 7b wound thereon. As shown in FIG. 2, magnetism generating portions 9 of the electro-magnet 8 are adjacent to the ion deflection pathway 5. Ions (charged particles) in the ion beam 4 move through the ion deflection pathway 5 to receive bending action in directions perpendicular to directions of magnetic field lines G in a magnetic field of the electromagnet 8 with a result that the ion beam 4 is bent in the ion deflection pathway 5. In this respect, generating a strong magnetic field can cause the ion beam 4 to be bent with a greater deflection angle (90° in FIG. 1) with a result that ions with mass less than that desired are bent earlier and collide with a smaller-radius side inner peripheral portion of the ion deflection pathway 5 for separation whereas ions with mass greater than that desired fail to be fully bent and collide with a larger-radius side inner peripheral portion of the ion deflection pathway 5 for separation. This enables only targeted ions to be accelerated by ion acceleration electrodes 10 at the other end of the ion deflection pathway 5 and to be taken out through an outlet 11.
The take-out ion beam 4 from the ion mass separator 1 is used in an ion doping apparatus where operations such as convergence of the ion beam 4 may be effected as needs demand and then irradiation to a substrate 12 to be dealt with is effected to implant the ions into the substrate 12. In the ion doping apparatus 13, ion doping is effected over an extensive surface of the substrate 12 through movement of the substrate 12 or electrical scanning of the ion beam 4.
However, in the above-mentioned ion mass separator 1 using the electromagnet 8 having the iron core 7a with the solenoid 7b wound thereon, magnetism generating portions 9 of the electromagnet 8 must be adjacent to the ion deflection pathway 5 for generation of the uniform magnetic field lines G so as to form a stable and strong magnetic field for bending of the ion beam 4; therefore, magnitude X of the ion beam 4 in FIG. 2 in the direction of curvature radius may be increased to some extent by increasing in size the electromagnet 8 while widthwise magnitude Y shown vertically in FIG. 2 cannot be increased. More specifically, increasing the widthwise magnitude Y would require spacing between the magnetism generating portions 9 to be increased as shown in FIG. 3; such increased spacing between the magnetism generating portions 9 would lead to failure of forming an uniform magnetic field in the ion deflection pathway 5 due to deformation of the magnetic field lines G outside, resulting in nonuniform bent of the ions and failure of obtaining a stable ion beam 4. Thus, there have been no ion beam 4 larger in size and uniformly ion mass separated since increase of the widthwise magnitude Y is unavailable.
The present invention is made to solve such problems in the conventional apparatuses and has its object to provide an ion mass separation process, an ion mass separator and an ion doping apparatus, enabling uniform ion mass separation in an ion beam larger in size.